The virus sweeping across China could knock 1.2 percentage points off the growth rate of the world's largest economy, S&P Global Ratings estimated, according to Bloomberg.

The SARS-like coronavirus has infected around 900 people and killed 26, prompting Chinese authorities to lock down a dozen cities and restrict the movements of 30 million people. While the World Health Organization declined to categorize the outbreak as a global health emergency on Wednesday, analysts fear it could spread far and wide this weekend as hundreds of millions of people travel to celebrate Chinese New Year.

The International Monetary Fund currently expects China to grow 6% this year. The S&P estimate, which assumes a 10% drop in consumer spending on discretionary goods and services such as transport and entertainment, suggests that could fall to 4.8%. The Chinese economy already slowed to 6.1% growth last year, down from 6.6% growth in 2018.

"It's potentially huge," Neil Wilson, chief market analyst of Markets.com, told Business Insider. "We simply don't know what the impact or even the potential impact could be. We only have SARS in 2003 to base assumptions on."

China's real GDP growth slowed from 11.1% in the first quarter of 2003 to 9.1% in the second quarter, suggesting SARS had an impact of about 2 percentage points, according to CEIC data.